Source Depth of Three-minute Umbral Oscillations. (arXiv:2003.10542v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Cho_K/0/1/0/all/0/1">Kyuhyoun Cho</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Chae_J/0/1/0/all/0/1">Jongchul Chae</a>
We infer the depth of the internal sources giving rise to three-minute umbral
oscillations. Recent observations of ripple-like velocity patterns of umbral
oscillations supported the notion that there exist internal sources exciting
the umbral oscillations. We adopt the hypothesis that the fast
magnetohydrodynamic (MHD) waves generated at a source below the photospheric
layer propagate along different paths, reach the surface at different times,
and excited slow MHD waves by mode conversion. These slow MHD waves are
observed as the ripples that apparently propagate horizontally. The propagation
distance of the ripple given as a function of time is strongly related to the
depth of the source. Using the spectral data of the Fe I 5435A line taken by
the Fast Imaging Solar Spectrograph of the Goode Solar Telescope at Big Bear
Solar Observatory, we identified five ripples and determined the propagation
distance as a function of time in each ripple. From the model fitting to these
data, we obtained the depth between 1000 km and 2000 km. Our result will serve
as an observational constraint to understanding the detailed processes of
magnetoconvection and wave generation in sunspots.
We infer the depth of the internal sources giving rise to three-minute umbral
oscillations. Recent observations of ripple-like velocity patterns of umbral
oscillations supported the notion that there exist internal sources exciting
the umbral oscillations. We adopt the hypothesis that the fast
magnetohydrodynamic (MHD) waves generated at a source below the photospheric
layer propagate along different paths, reach the surface at different times,
and excited slow MHD waves by mode conversion. These slow MHD waves are
observed as the ripples that apparently propagate horizontally. The propagation
distance of the ripple given as a function of time is strongly related to the
depth of the source. Using the spectral data of the Fe I 5435A line taken by
the Fast Imaging Solar Spectrograph of the Goode Solar Telescope at Big Bear
Solar Observatory, we identified five ripples and determined the propagation
distance as a function of time in each ripple. From the model fitting to these
data, we obtained the depth between 1000 km and 2000 km. Our result will serve
as an observational constraint to understanding the detailed processes of
magnetoconvection and wave generation in sunspots.
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